I was last in the mums' race two years running (or not) so now I'm not allowed to take part any more.

My kids are pretty embarrassment proof, though, having heard all my horror stories about how my father used to mortify me - knowing Grandpa, they can well imagine it. Even attending a poetry reading didn't bother them - mainly because my contribution was downright obscene (and therefore, axiomatically, cool).

As I tell my offspring: "I feed you, clothe you, send you to school, pay for you to get your teeth fixed. If the only joy I get out of this relationship is embarrassing you occasionally, then you have little to complain about."

When taxi-ing my children and their friends, and someone's just finished speaking, I look in the rear-view mirror, there's a glorious pause, then I say 'we know a song about that, don't we children?'

It's improved over the years as they anticpate it now, so it's more like:
(pause)
'We know a...'
'MUUUUUUUM!!!'

(c) those two comedians who haven't been seen out and about much lately who used to dress up as clown kids' TV presenters and say 'we know a song about that, don't we boys and girls' when the other one said something filthy. Hale and Pace, that's the chaps.

My daughter came back from her boyfriend's a week or so ago.
I had the place to myself.
When she sat on the sofa I just said "you'll never guess what me and (name withheld to protect dignity) did there on Saturday afternoon...."
She screamed and went to her room....
Job done.

I was in Waterstones with my sons recently. I picked up the Viz Profanisaurus and started reading it. After I laughed out loud a few times my eldest sort of hissed "Dad, either put it down or bloody buy it".
Other than that, generally any reference to the occasions on which they were conceived will do it. For instance, last time we had a power cut, we looked at our eldest and said "we'd best be careful - look what happened last time this happened".

My son is on the cusp of puberty. Diving out of the car outside of his very posh school while dressed in velour trakky bottoms, scabby fleece and flip flops to say goodbye at 8.30 in the morning generally works. And if necessary, answering the door to his friend's posh mum with a duster and can of Mr Sheen in one hand, marigolds in the other and cigarette hanging out the corner of my mouth does the trick.